1) Field of the Invention
The present invention relates to a technology for performing magnetic recording in a medium.
2) Description of the Related Art
Recently, as a storage capacity of a computer is increased, the storage capacity of a magnetic recording apparatus such as a hard disk drive (HDD) tends to increase. To increase the storage capacity of the magnetic recording apparatus, it is necessary to perform the recording in higher density by making a finer column of recording magnetic domains in a magnetic recording layer, which is formed by a signal magnetic field generated from a magnetic head. A perpendicular magnetic recording method is generally known as the method for recording the finer column of recording magnetic domains.
In the perpendicular magnetic recording method, the recording is performed by magnetizing the recording layer of a magnetic recording medium in a direction perpendicular to a plane of the recording layer. However, in the case of the extremely high recording density more than 100 Gbit/in2, recording action into adjacent tracks occurs by side fringing generated from a side face of the magnetic head, which results in recording failure and reproduction failure.
Therefore, the so-called discrete track type of magnetic recording medium has been proposed. In the discrete track type of magnetic recording medium, non-magnetic tracks made of a non-magnetic material are formed in a circumferential direction of the recording layer of the magnetic recording medium, and data is recorded only in magnetic tracks made of the magnetic material. In the discrete track type of magnetic recording medium, since the non-magnetic track is provided between tracks, there is an advantage that the data is prevented from recording in the adjacent tracks to realize good recording/reproduction characteristics.
In the conventional magnetic recording apparatus, generally a thin film inductive head is used as a recording head that records the data in the magnetic recording medium. An MR (magneto-resistance effect) head is used as a reproducing head that reproduces the data from the magnetic recording medium. Each head is mounted on the same slider to form a composite head. In a rotary type of drive structure, the composite head is supported at a tip of a head actuator, and the composite head is controlled so as to be moved in a radial direction crossing the magnetic track of the magnetic recording medium to be positioned at the desired sector. A servo area is provided in a recording surface of the magnetic recording medium. In the servo area, positional information such as a track position and a sector position is recorded in a track direction at predetermined intervals.
FIG. 26 is a schematic diagram that depicts the structure of the recording surface and the composite head of HDD that is of the discrete track type of magnetic recording medium having a servo area 103. In this case, the magnetic recording medium is the discrete track type having the non-magnetic track between the magnetic tracks, and each sector 104 includes a discrete area 101 and the servo area 103. The discrete area 101 includes the magnetic track 202 in which the data can be recorded and the non-magnetic track 201 in which the data can not be recorded. The magnetic track 202 is formed by the magnetic material. The non-magnetic track 201 is provided between the magnetic tracks 202. A magnetic head 210 has the structure in which a recording head 211 and a reproducing head 212 are separately arranged. Therefore, a recording center position of the recording head during recording the data and a reproducing center position of the reproducing head during reproducing the data is usually different from each other. When a signal is reproduced, the reproducing head is positioned at the track center position with respect to a predetermined target track. However, when the signal is recorded, the recording head is positioned while shifted from the track center position.
On the other hand, when the recording head is positioned at the track center position, the reproducing head is positioned while shifted from the track center position. The amount of shift has a different value in each track, because an angle of the magnetic head is changed depending on the target track.
Accordingly, to be able to respond to the target track, it is necessary to previously measure the offset amount that is of the amount of shift between the center position during the recording and the center position during the reproduction and to perform offset amount control which corrects the center position during the recording and the center position during the reproduction using the measured amount.
To measure the offset amount, the reproducing head is positioned at the track center to record a measurement pattern indicating the recording head position. Then, the data is reproduced while the reproducing head is gradually moved, and the optimum offset amount is determined by deciding the offset amount in which amplitude of the reproduction signal becomes maximum or the center position of an offset range in which the amplitude of the reproduction signal becomes maximum (For example, see Japanese Patent Laid-Open No. 9-45025).